With Apple’s latest Operating system (OS), macOS Sierra 10.12 , releasing later today, there is some concern about the compatibility of older Adobe products such as Lightroom 5. We, therefore, advise our students which are using the old software on macs, to rather hold off on updating, since there have frequently been compatibility errors in past. The following link shows a list of some of the compatible and incompatible software, that has been tested by the Mac Community: Mac Sierra 10-12 Compatible Apps
It should also be noted that not all Macs will be able to support Sierra. To see if your Mac is compatible with the new OS, click on the apple icon in the top left and choose About this Mac. If your Mac shows (Late 2009) or later, then it should be able to support Sierra.